In certain contexts, there is a need to achieve a short, powerful rotary motion in a definite direction. In certain cases, this can be quite unproblematic if the available drive source has a corresponding motion characteristic. However, this is not always the case. It may occur that the available drive source is of such a kind that it carries out rotary motion in one direction as well as in the other direction.
There are also situations where the drive source included does not immediately achieve a required powerful torque for the necessary short period. It may also occur that both of these imperfections occur simultaneously as far as the available drive source is concerned.
One example of such a situation is when operating a diverter switch in an on-load tap changer for controlling the voltage of a transformer. In this case, it may be advantageous that the operating motion always occurs in the same direction, and it should occur for a relatively short period of time. Usually, the drive source for such a diverter switch is in the form of the drive shaft that operates the selector switch, that is, the mechanism that sets the connections to new tap points in the winding of the transformer when a change of voltage is to take place. The drive shaft of the diverter switch rotates in different directions in dependence on whether it is a question of increasing or reducing the voltage of the transformer.
From WO 89/08924, a motion-transmitting mechanism is previously known, which is able to transform a rotary motion in one or the other direction into a unidirectional motion while at the same time concentrating the rotary motion with respect to time. The unidirection of the motion takes place by a special design of the spring, and the element directly cooperating therewith, that accumulate the energy and concentrate the rotary motion.
From SE 0401712-5, a motion-transmitting mechanism is previously known, which transforms a rotary motion in one or the other direction into a unidirectional motion which via, inter alia, a gear-wheel mechanism and shafts, transfers the rotary motion into an energy-storing system in the form of a spring unit. When the spring unit with a locking device is released, motion is transferred to a final shaft. The diverter selector switch and the whole drive package are surrounded by transformer oil.
This mechanism is dependent on a mechanical return of a rotary pulse from the spring unit to the retaining pawls of the gear wheels in order to ensure that these will mesh with each other. Under extreme temperature conditions, for ex-ample at very low temperatures of the oil (−40° C.), the viscosity of the oil is relatively high, and the returned rotary pulse may become too weak to ensure that the ratchet gearing will enter into a locking position.
The present invention seeks to provide an improved device for transmitting rotary motion, wherein the transmission function is ensured also under extreme temperature conditions.